In recent years, telematics devices have been provided to vehicle users by entities, such as insurance companies, trucking companies, and package delivery companies, to monitor vehicle operations by the respective vehicle users. When connected to a vehicle's on-board diagnostics port, the telematics device detects vehicle operating signals and collects and records operational data, such as vehicle speed, braking data, vehicle acceleration, maintenance and other operational data. The collected data may be sent to the entity, which can analyze the data e.g. to determine the driving habits of the vehicle users and an overall safety state of the particular vehicle. For example, an insurance company may use the collected data to determine the risk associated with a particular user and vehicle, and may adjust the user's insurance premium based on the collected data. The collected data may be retrieved, processed, and provided to the entity on a regular basis by a third party from the telematics device.
In order to avoid the collection of data, a user may disconnect the telematics device from the on-board diagnostics port. The telematics device receives power through a connection in the on-board diagnostics port. Disconnecting the telematics device from the on-board diagnostic port therefore not only disconnects the telematics device from the data source, but also disconnects the telematics device from its source of power. As a result, the disconnected telematics device does not collect any vehicle data and is unpowered. Afterwards, the user may reconnect the telematics device to the on-board diagnostics port. At least some telematics devices have the capability to detect such a disconnect period and provide indications to the entity that the telematics devices were disconnected for a period of time. Such a telematics device can also provide an indication of the duration of its disconnect time period, winch may be stored in memory. The indication of the duration of the disconnect time period may also be provided to the entity during an upload process.
For disconnect detection, the telematics device has an internal clock that starts when the telematics device is supplied with power (i.e. connected to the on-board diagnostics port). The telematics device synchronizes the internal clock to an external clock signal that may be received from different time sources, such as a global positioning system (GPS) satellite and a cellular network, such as a GSM/CDMA communication network. One or more of the external clock signals may be used to synchronize the internal clock. The telematics device receives clock signal updates from the different external time sources in order to prevent timing errors, for example, from time drift of the internal clock time value. The telematics device has an internal clock that updates a stored system time at a set interval. The external clock updates are received also received at a set interval that is greater than the internal clock update interval. The stored system time is replaced with the time provided by the external clock updates, and the internal clock synchronizes to the replaced system time. However, the accuracy of the updated clock signals from the different external time sources is unchecked, so an inaccurate external clock update signal, may have an adverse financial effect on the entity and/or the vehicle user.